Venting carbon dioxide

The major disadvantage of the single-cycle system to date has been the diflSculty of predicting the cleaning efficiency of the cosol-vent/carbon-dioxide mixture at the various operating conditions. 

There are subtle reasons why venting carbon dioxide from trash incineration is of far less concern than the venting of the same gas from fossil fuel combustion reactions. Large portions of the carbon compounds in domestic trash are paper and food wastes. Only a few years ago the carbon contained in these plant products was part of the atmosphere. On a long-term basis, returning this carbon to the atmosphere has no effect on the overall carbon dioxide balance it simply speeds up the rate of recycle of carbon from plant material to the biosphere. 

In an effort to keep these events from recurring, scientists have constructed a piping system that slowly vents carbon dioxide from the lake hottom, preventing the huUdup that led to the tragedy. 

A plumbing system slowly vents carbon dioxide from Lake Nyos. 

This carbon dioxide-free solution is usually treated in an external, weU-agitated liming tank called a "prelimer." Then the ammonium chloride reacts with milk of lime and the resultant ammonia gas is vented back to the distiller. Hot calcium chloride solution, containing residual ammonia in the form of ammonium hydroxide, flows back to a lower section of the distiller. Low pressure steam sweeps practically all of the ammonia out of the limed solution. The final solution, known as "distiller waste," contains calcium chloride, unreacted sodium chloride, and excess lime. It is diluted by the condensed steam and the water in which the lime was conveyed to the reaction. Distiller waste also contains inert soHds brought in with the lime. In some plants, calcium chloride [10045-52-4], CaCl, is recovered from part of this solution. Close control of the distillation process is requited in order to thoroughly strip carbon dioxide, avoid waste of lime, and achieve nearly complete ammonia recovery. The hot (56°C) mixture of wet ammonia and carbon dioxide leaving the top of the distiller is cooled to remove water vapor before being sent back to the ammonia absorber. 

Calcium C rbon te. Calcium carbonate, like R2O2, affects sulfuric and oleum consumption in the HF process. Sulfuric acid loss is approximately 0.98% H2SO4 for each percentage of CaCO. The carbon dioxide evolved by the reaction increases the noncondensable gas flow, and because it carries HF, contributes to yield losses in the vent stream. 

These equations are based on the thermodynamically stable species. Further research is needed to clarify the actual intermediate formed during overcharge. In reahty, the oxygen cycle can not be fully balanced because of other side reactions, that include gtid corrosion, formation of residual lead oxides in the positive electrode, and oxidation of organic materials in the cell. As a result, some gases, primarily hydrogen and carbon dioxide (53), are vented. 

The ethylene oxide recovered in the desorber contains some carbon dioxide, nitrogen, aldehydes, and traces of ethylene and ethane. In the stripper the light gases are separated overhead and vented, and the partially purified ethylene oxide is sent from the bottom of the stripper to the mid-section of a final refining column. The ethylene oxide from the refining section should have a purity of >99.5 mol %. The final product is usually stored as a Hquid under an inert atmosphere. 

The noncondensable gases eventually reach the condenser (unless vented from an effect above atmospheric pressure to the atmosphere or to auxiliary vent condensers). These gases will be supplemented by air dissolved in the condenser water and by carbon dioxide given off on decomposition of bicarbonates in the water if a barometric condenser is used. These gases may be removed by the use of a water-jet-type condenser but are usually removed by a separate vacuum pump. 

I. Gas movement. In most cases, over 90 percent of the gas volume produced from the decomposition of sohd wastes consists of methane and carbon dioxide. Although most of the methane escapes to the atmosphere, both methane and carbon dioxide have been found in concentrations of up to 40 percent at lateral distances of up to 120 m (400 ft) from the edges of landfills. Methane can accumulate below buildings or in other enclosed spaces on or close to a sanitaiy landfill. With proper venting, methane should not pose a problem. 

Unvented kerosene and gas space heaters leaking chimneys and furnaces back-drafting from furnaces, gas water heaters, woodstoves, and fireplaces automobile exhaust from attached garages environmental tobacco smoke. Humans are normally the main indoor source of carbon dioxide. Unvented or imperfectly vented combustion appliances can also increase indoor COj concentrations. 

Another problem is when the carbon dioxide content of natural gas is too high and must be lowered to produce pipeline-quality gas. Although the current practice is to vent this CO, sequestration of CO, in underground geologic formations is being considered. Already, in the Norwegian sector of the North Sea, CO, has been injected into saline aquifers at a rate of 1 million tons a year to avoid... 

Example 9-13. Desdgn a Packed Tower Usii Caustic to Remove Carbon Dioxide from a Vent Stream... 

Air vents are most effective when they are fitted at the end of a length of 300 mm or 450 mm of uninsulated pipe that can act as a collecting/cooling leg. Air is an excellent insulating material, having a thermal conductivity about 2200 times less than that of iron. The last place where it can be allowed to collect is in the steam space of heat exchangers. Further, as it contains oxygen or carbon dioxide, which dissolve readily in any subcooled condensate that may be present, the presence of air initiates corrosion of the plant and the condensate return system. 

In large and extensive industrial process plants, it is not unusual to find unvented condensate receivers or reboilers at the end of a long steam-condensate line. These vessels tend to act as collection and storage points for carbon dioxide, which may redissolve in condensate. These satellite stations should be vented and receive an amine booster feed. 

Shikazono, N. and Kashiwagi. H. (1999) Carbon dioxide flux due to hydrothermal venting from back-arc basin and island arc and its influence on global carbon dioxide cycle. 9th Annual V.M. Gohl.schmidt Conference, August 22-27. Harvard, Abstr., p. 272. 

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